I used to be scared of asking questions at school in case I looked stupid, but then I would end up looking stupid because I hadn't asked the question. The worst case scenario is that your question is a silly one and someone might giggle or the teacher might grumble. On the other hand, if you ask a question, it shows that you are interested, listening and thinking about the topic. It is also better to ask a question and check that you only have to do questions 3 and 4 for homework, rather than staying silent and doing questions 1-10 because you weren't sure. 99% of the time it's better to ask the question.